Telephone system



June 12, 1928. 1,673,367

C. E. LOMAX TELEPHONE SYSTEM Filed Jan.2, 1925 ets-sheet 2 E Eng June 12, 1928. 1,673,367

c. E. LoMAx TELEPHONE SYSTEM Filed.Y Jan. 2, 1925 5 Sheets-Sheet 5 HTH.-

Patented June 12, 1928.

UNITED STATES PATE @anni Application filed January The present invei'ition relates in general to telephone systen'is, but lis particularly coin eerned with telegihone equipment 'for use in private ai'iton'iatic exchanges which are equipped with trunlring facilities iiiei'initting automatic exchangesubscriber on calls from the main automatic exchange.

Another feature lies in the provision ot special night service, which is given after the attendant at the private automatic e3;- change leaves her position.

Another feature has lo do with an iinproved impulse repeating circuit shown in a selector repeater. f e

The cord circuit shown also contains novel supervisory circuits7 which `will bebrouglit out in the description and claims.

The foregoing features are attained by the circuits diagrauiniatically illustrated in the accompanying drawings which. when laid out with Fig. 3 at the leiit of Fig. 2 and with Fig. 1 above Figs. 3 'and 2 with the corresponding lines .in alignment, show sui'iicient of a telephone systein to enable the invention to be understood when the description is carefully followed.

Fig. 1 `shows a tyliie ordinarilyuscd bv inat-ic telephone systeingaline swii subscribers oi auto a selector repeater'D of `the vvell known vertical and rotary type.

Fig. 2 illustrates'a trunk circuit T` For es tablishing calls between the private auto- Afniatic exchange andV the inain automatic exchange. This e also .shows a hey K used when night service is given, and a key l and jacks lL-J1@ used for conference service.

Fig. 3 shows a cord circuit (l, which is one ailing substation of the h C oity the vvell known continuons rotary type, and

i925. serial No. e1.

Fig. 4i shows a. pair of relays used in addition to those shown in Fig. f2 under condi tions which will be explained later.

lt is believed that all features of theinyention can beniost clearly explained by describing the various operationswhich take,r place during the process oif setting up connections. This has been done, the separate classes oit' connections being identified by appropriate headings. y g

In order to simplify the descriptions which follow, the `abbreviation 13. A. X. is used for the Words private automatic ex change and tdie abbreviation BLA. X i is used for the words mainl automatic exchange (laffe from Hic P. A. X. to Hi@ lll .i1/l. i

Then the receiver is removed kat substation A a circuit is completed `lor the line relay 125 of the line switch C. This circuit extends from grounded baci; contact and armature 20, lineconductor 12, the sivitchy hooi; of substation A and its upper contact. through the receiver and ti'ansniitterycalling device springs S, line conductor 1.1 armature ,.19- and its resting contact, and the winding ol' relay .13 to battery. Relay 13, upon operating, at its arinatliire 14; preiares a circuit for switchine rela 16 and at i its arnial'ure 15 connects the'test Wiper 23. to the inotor magnet 21 via armature v17.r and its resting Contact, and the interrupterV springs oi' the niotor magnet. `The inotor niagnet no'vv operates long as the Wiper engages grounded or busy contacts` In the present case it is assumed that the trunk comprising conductors 28, 29 and 30 extending to theselector repeater D, is the first idle trunk engaged by 'the Wiper 23, at which time the formerly shunted switching relay, 16 is energized in series with the inotor magnet 21. Magnet 21 does not energize over` this circuit due to the comparatively high resistance of relay 16. vRelay lli, at armatures 19 and 20, disconnects the line relay 13 and groundiand at the frontcontacts of these armatures extends the calling line to the line relay 31 ot the selector repeater D, and at its armature17an l its front contact prepares a holding .Circuit for switching relay 16j which will be completed by relay 234e of switch D before the slo'vrre-` lease relay 13 becomes deenergized-- As soon as the calling line is extended to the con- CRF'GLd-ATION OF DELAWARE.

ltl

ductors 28 and 30, line relay 31 energizes, at its armature 32 prepares an impulsing circuit which will be described later. and at its armature 33 completes a circuit tor slow release relay 34;. Relay 3-1- encrgizcs. at its armature 36 opens a point in the release magnet circuit, and at the tlont contactV olf. thisI armature preparesl an operating circuit lor the vertical magnet 1T and slow release relay 4Q. and at'. its armature. 3.3 grounds conductor 29 in order to maintain the switching re lay 16 energized after the release ot relay 13. Everything is now in readiness for the subscriber at substation A to dial the digit which is effective to position the wipers of the selector repeater' D into engagement with an idle trunk extending to the M. A. X..

In the present case the bank contacts in the eighth level ot' the switch D are connected with trunks extending to the M. A. X. The subscriber at substation A therefore operates his calling device in accordance with the digit S. causing the line relay 3l to drop back a like number of times. Each time line relay 31 deenergizes ay circuit is completed for the vertical magnet t'i' and the slow release relay 42 in multiple. Relay l2 remains energized throughout the impulse series. while vertical magnet t7 operates in the usual manner to more the wipers 55, 5G and 57 opposite the eighth level of bank contacts. As soon as the switch shaft is elevated one step, otl` normal springs 37 and are closed. The closure ot' springs 37 is, however. without eti'ect at this time, due to the energized condition of slow release relay Si. The closure of oli` normal spring 53 completes a. circuit for stepping relay 18. This circuit extends by way of grounded armature and its working Contact, release trunk conductor 29. springs controlled by armature armature t1 and its working contact. rotary oli' normal springs 52, ott normal springs 523, and the winding ot stepping relay 48 to battery. Relay 4S, upon operating` at its armature 50 and its working Contact prepares an operating circuit for the rotary magnet 51. and at its armature 4.9 completes a locking circuit for itsel'l extendingthrough interrupter springs 50 and a Shunt circuit about the winding of switching relay 58. Shortly tollowing the termination of the transmission of the tirst series of impulses. relay t2 restores, and. in so doing. at its armature tt completes a circuit for the rotary magnet 51 by way of grounded conductor 29. springs controlled by armature L15, armature 4t and its resting Contact, working contact and armature 50, and the winding o'l magnet 51 to battery. Magnet 51 energizes to rotate the Wipers ot the switch D one step and at its interrupter springs 59 opens the previously' mentioned locking circuit for the stepping relay e18. This relay. accordingly, deenergizes, at its armature t9 breaks its own locking circuit, and at its armature 5t) breaks the initial energizing circuit of magnet 51. The further operation ot the switch D now depends on the busy or idle condition oli the trunk engaged by the test wiper 5G. l't` the lirst` trunk is busy ground will be. present on the test contact engaged by wiper 5G, short circuiting the .switching relay and preventing it trom operating in series with the stepping magnet 218. lnstead, the stepping relay t8 will be energized by ground supplied over wiper ati via armature Mrt5 and its resting contact and inter rupter springs 5t) to again complete an operating circuit for motor magnet 5l. Mag net 51, accordingly, energizes to step the wipers into engagement with contacts associated with the next trunk. It will he.

seen 'troni this that the stepping relay t8 and the rotary magnet 51 operate alternately as long as the test wiper 5G engages busy test contacts. its soon as the wiper .Sti comes into engagement with an ungrounded bank contact, which we will assume is contact t'rl. switching relay 5F will be no longer short circuited and will therefore energize in .series` with the stepping relay t8. llowever. due to the high resistance ot relay the stepping relay 1S does not energize at this time. telay 5S. upon operating, at armature l-ti disconnects the vertical magnet 4T to prevent its operation on subserulentl impulse series. and at armature 45 removes` the grounded conductor Q9 Vfrom connection with armature 14, disconnects the wiper titi trom connection with the stepping relay ful. and instead connects this wiper directly to the grounded conductor 2l). ltelay 5S also at its armature 5t completes a bridge acros.V`l the outgoing end of the trunk. This circuit will be, traced subsequently. 'the grounding of wiper 56 ot the switch l) makes the bank contact ('l and its multiples busy to all other switches having access to the same group ot trunk lines. The grounding o1' bank contact GQ i lso causes a circuit to be completed orer conductor T2. armature 95 and its resting contact'. to the busy visual .signal 12H at the attendantsI position.y and the trunk relay Fifi in multiple to battery. The visual signal. ot" course, informs the attendant; that the trunk has been taken for use. Relax4 HH. upon operating. at its armature lttl discouneets the ring-down relay 04 and the polarized relay 8G trom in bridge ot the trunlconductors 8l and at. armature fl.) breaks a point'l in the locking circuit, llor thc ringdown relay,` and at armature llltl remove.: ground from conductor 8T so that relay HI will not energize upon deenergization ot' the polarized relay 80. which decnergize:-: as a result of its circuit being opened at armature 101.

The bridge placed across trunk conductors 81 and 82 by the operation ot' arlnature lue llU

of switching relay 58 will now be traced. This bridge extends by way ot trunk conductor 81, conductor 71, bank contact 61, wiper 55, front contact and armature 5-1, mature 32 and its t'ront contact, impedance 39, wiper 57, bank contact 63, conductor 7 conductor 83, conductor 85, and the trunk conductor 82.l The trunk conductors 81 and 82 terminate in a line switch identica-l to the line switch C, and, therefore. immediately upon the closure oit the bridge vinst described the line switch will immediately function to extend the trunk conductors into connection with a selector switch which may be of any well known two-wire type.

The calling subscriber may now operate his calling device to transmit the first` digit of the called subscribers number. This time, at every deenergization of line relay 31 it opens, at. its armature 32, the circuit for the line relay of the seized selector switch, causing that switch to advance its wipers into association with bank contacts in which conductors tern'iinate enti-aiding to a desired group of second selectors or connectors, depending on the size ot the M. A. X. It will be noted that on each deenergzization of line relay 31 a circuit is completed for slow release relay 42. This relay, therefore, remains operated during the entire impulse series, and at its armature 43 connects the non-inductive resistance 67 in parallel with impedance 39. The non-inductive resistance 67 is provided to prevent the line relays of the subsequently operated switches from momentarily deenergizing, which would result in the transmission of an extra. impulse. This may occur when a. direct short circuit is removed from around the impedance 39 upon deenernization of relay 42 due to the inductance of impedance 39. Howeveigby placing a non-inductive resist-ance in mult-iple with' the impedance sufficient current flow is permitted to maintain the impedance partly saturated so that the current tiow in the line relay circuit is not materially affected b y the removal of resistance 67.

The further operations which take place when a connection is established with an M. A. X. subscriber are old and well known, and. therefore. no attempt is being made to show or describe these operations or circuits. TWhen conversation is conniletcd releer@ is broun'l'it about in the usual manner. The line relay 31 ot the switch D restores upon replacement of the receiver at station A on its switch-hook. Shortly following the rclcase of .relay 31 slow release relay restores; at its armature 35 removes .around trom the holding` circuit .oit lino switch C, permitting this switch to restore to normal, and at armature 36 completes a circuit for the release magnet Upon release ot the switch D. aground is removed from conductor n 72, and visual signal 128 at 4the attendant Culte ,trof/a P. A. X. subsmzfbers to the l attendu/m5 operator.

Then a P. A. X. subscriber desires connection with the attendant operator, such connection is completed by the subscriber diallingn the digit O, which results in the switch D selecting; a` trunk in the tenth level. Assumingt the trunk comprising conductors 78. 79 and 8O to be idle when the wipers ot the selector repeaterD becomesassociated therewith, no ground will be present on the test Contact andthe switchingr relay 58 of the `selector repeater D will switch the connect-ion through in the previously described manner. T and the repeating' coils 124 and 125 are in bridge ot' conductors 78 and 80, which now extend to and through the substation A.. Consequently relay 123 energiZes and in turn causes the 'energization of slow release relay 121. Relay 121, upon operating, at its armature 104 applies ground to test conductor This ,ground is oif no utility when selector repeaters are used, but is provided to feed ground back over conductor 7 9 in installations where ordinary selectors are used. Relay/"121 also, at its armature 105. closes a bridge across conductors 147 and 148 'tor operating the call signal relay 151 at the attendants position. This circuit 'extends by way ofground, upper windinfr of relay 151. armature 156 and its back contact,yconductor 74, resting contact and spring` 133 ot key K, conductor 144,wind inn' 126 ot the repeating coil R. armature and its working' contact, windingV 127 ot the repeating' coil, conductor 146, spring: 137 and its resting' contact, conductor 76, resting contact and armature 157. andthe winding of relay 151 to battery. Relay 151 operates over this circuit and completes a, ,circuit for the call. signal lamp L2.

The attendant upon notingr the lighted condition of lamp L2 will proceed to answer the call by inserting' the plug P into the answering jack J2. This causes i ack springs 158 to be closed, resulting` in theenergization oi cut-otl` relay 154 and sleeve relay 167. Relay 154. upon operating. at its armatures 156 and 157 disconnects line relay `151 from in bridge ot conductors 74 and 76. Sleeve relay 167 in thccord operates to disconnect the tertiary `winding ot the attendants head set and to complete the continuity of the tip conductor.

A circuit tor supervisory relay 159 is now completed 'troni ground. resistance 18?. back contact and armature 172. lower winding;v of impedance coil 168. arn'ieture and back contact of relay 166, resting contact and spring The relay 123 of the trunk 161 of key K. ring of plug P, ring terminal of jack J2 to eonduetor 71'. over the previously traced path to eonduetor Tit. tip aide of jack JL'. tip of plug P. spring 1nd ot' key 1': and its resting eontaet. winding of relay ltl, armature o1 relay ltiand its working Contact. upper winding o1l impedance ttil. armature 171 and its resting enntaet. and resistanee 185 to battery. The, operation ot` relay 159 results in the operation otf relay 162 whirh` at its armature ltl. eonneet noninduetiye resistanee 1.5i in multiple with re lay 159 to improve transmission and at armature 16Tt opens a point in the eireuit ot supervisory lamp L3.

Url/la bett/teeny I). r1. .valmer/'MAQ rio' t/ie attendu/ifa pea/fion.

As hereinbetore pointed out. ordinarily. the. 'arious P. A. X. Subrwribers will eet up connections between themselves without the assistanve of the attendant operator. floweyer. it tor any reason a l). A. X. antiseriber desires to establish a eonneetion to some other l). A. X. subscriber via he atteuiilantk` position. he may do so by ealling the attendant in the usual manner. and requeat the attendant to lall the desired iarty. rlfhe lall is answered. oit eourse. by the. attendant. placing the plug P o1E her eord into the iatk auch as .12. ot: the trunk over whieh the :all Vas set up. llle will asa-unie that a l). subscriber has ealled the attendant. and that the lQubseriber at substation A is desired. .\eeordingly, the attendant operator testa the eondition of the desired line by touching' the sleeve. of jack il with the tip ot .i plug o1 ay cord not in use to determine the bua); or idle condition of substation It. lt the :alled line is busy the attendant' will inform the subscriber. s'auming. however. that the, station A is idle. the atteni'iant insert-s the. plug 1) into the jat-lt d". ln orde: to eliminate the poasibilityY o1' opera'ing the line relay ol lwitch C. the tip eonduetor normally held open at armature 15% oll eutotl' relay 1t. This makes iti neeessarj.' that the out-oill relay ope ates` before the tip I"onduetor lan be eut through. 'l`he elosure o1' jaek springs 1551 eauee` ground to be applied to eonduet'or 2b. to energize the int-oil' relay 115 o1 the line .switch C. Since the terminal ot sleeve relay 1(39 is eonneeted with ground. and the sleeve eontaet ot the plug l is now grounded by the sleeve ot `ia'k Il. this. relay will nothe operated. The attendant operator may now Signal the. desired suhsoriber by operating ringing key lt" momentarily. She may then operate lier liatening key l@ to make eertain that tlie called subscriber has reaponded. 1n this connection, talking battery is supplied to the subscriber at substation A. by the battery and ground supplied through the back contact and armatures 171 and 172 ot the sleeve relay 160. and the uppe anl lower windingsA ot' the il'npedanee, eoil 1.11% whieli are now in bridge o1I the tailed line. l)i.-ironnei:ti superyieiou is provided by the lamp lf" which heroines lighted when the ealling aubeeriber reiilaees his reeeiyer.

ltt the attendant operator i'lesire.-. :lhe may :ret up eallf: between the l). X. f-ub.-eribers eo that the l upervifsiou o1' the eall is under rontrol ot' the e:lled ub,--'eriber. ln ui-h eaee when a all rome` in the attendant either originally answer:`4 the e: ll by inseriing the plug l) in jat-k il: and then reverses the eord when he learn1 that another l). It. X. .-'1ilia"1'ilier is desired. or answers the eall by in.-ertingl the plug l into iaek cla. Vln either ease when plug 1) ie inserted in jaek .l2 relay 1G?) not oi'ierated. duo to ground Supplied by api-ings 15S. Nine-e the relay 111i is not` operated the attendant may use, the same oord to tert the ealled line. lilhen the ealled subseriber answers relaya 1.35) and lti energize. to extinguish superiisory lamp L3.

On eertaiu oet-anions it may be desirable to have the attendant Set up eonneetiom` to sub- :erilrera o'l the X. le will :resume thatI the subseribe at` xsubstation seta` up a eoniieetion. in the manner hereinbel'i'ire deeribed, to the attendant operatous iioeition. requesting the attendant operator tio extend the xall to a Dit. i\. X. party. The attendant operator. upon noting that the trunk 'l` ia idle. inaerts the, plug 1) ot her eord t) in the .iaek l of the tlnnk T. Sleeve relay 1.0i) in the eord t). yiaual lQignal 12S. and relay SQ. ot the trunk 'l` are operated oye' a eii'euit extending l'roni ground. winding.r ot relay tot). sleeve of plug P. sleeve side ot jack Il. eonduetor SS). and the visual signal 128 and relay SS in multiple to battery. Relay 89. upon operating. atv its armature 1111 removesy the polarized relay tilt) and the ring'dlwn relay t'l-ttroni in bridge o1 ther outgoingr trunk eonduetori: S1 and H2. atl its` armature ttl() opemv a point in the operating eireuit ot relay 811-, and at. armature 9S) opens a point' in the loeking eireuit; of ringdown relay Qui. The relay 169 in the eord operates. and at ita armatures 171 and ,172 eonipletef; a direct eurrent bridge arroes the tip and ring conductors of the (ford. Sinee these eonduetor.` are in direet ronneetion with eonduetors 31 :1nd b2 ot' the trunk rl`. the. line switr'li in whim thi-rw eonduetowI terminate at onre exteuda the eoni'ieetion to a eeleetor of the tl. n\.. Y.. .laek springs H1 of the jaf'k .l are also closed now. and. Sine-e the polarized relay ot now deenergized. a eireuit is Completed extending- 'roni ground. working eontact and springs 81', conductor 87, resting tit) or ot) Contact and urinature 98, and the Winding of relay 8l te battery. Relay operates and at its armature applies ground potential. to conductor/i2. in order to inake the trunk 'l busy to the selector repeater D and other similar selector repeater-s having uccess to trunk T. The attendant operatorinay now el crate the ,ley l@ thereby con-` nectinp,a her heed-set and culling device S into operative relation to the cord, The at; tendant operator is nov.7 ready to Sist the switches ol' the M- A. X in accordance with the ntli'uber of the desired subscriber. Upon loi-wurd inovenient of the callingv device a" its eti' normal springs are closed, complete ine a circuit for the slow release relay 179 which, in turn, opera and at its armature 131 places a shunt about the attendants receiyer, und at its armature 180 completes circuit vic.. springs 176 of `rey K3 for the calling' device cont-rol relay 170. Relay 170, upon operating, bridges the calling device across the tip and ring conductor el" the cord in substitution for the bridge extending, through the impedance coil 16S. The process ot transmitting impulses over the conductors 8l and S2 to the various switches in the M, A. X, is well known and, therefore, need not 'further be described. lt is suf,-

lcient to point out that when the connection' is established talking buttery is supplied to the l). il.. X. subscriber vie the line relay ci the connector oi: the M. A. X. This battery also serves to operate the supervisory relay 159 which, or' course, remains energized as long; us the culling subscriber has his receiver eli' the hook. However, the culled subscriber muy recall the attendant operator by operatingl his switchhook, which results in battery in the trunk being revel-sed each `time the back bridge relay in the connector deeper- 'lhis causes supervisory relays 159 and ,62 to momentarily restore causing lauw L .te be flashed. When the converse.-

tion is completed disconnect supervision is also provided by the lanip L3. The calling sul criber, upon replacing his receiver,

cans s the disconnection and release of the varios ...witches set up in the P. A. X., While the :re invul ci the plug P from the trunk "uuses the switches in ,the M. il, iti. .cred to normal.

@e718 from M. A X. to P. A. X.

when said Subscriber extends. e, ,Connection t0 Sonie Subscriber 0f. the A- X. lt is believed, sutcient. te say that. when .he trunk conductors .S1V and 82 are seized the outfqlf relay et the line switch associated therewith is Operated to disconnect the nrmul battery and, ground connectens theret'rom- This @euses the vdeencrs,tetion et polarized 132: lay 86 in. the trunk circuit which upon re- Storing its armature r98, .Completes ebrcuit, for the Slow release relay 84. Relay 8.4, uren Operating', at ,its armature 95 dsceilllectsthe conductor 72 from connection With the visuel Signal 128 und. relay 85 and Connects it. to ground, thereby making' the trunk T busy to all selector repeaters, such as D, at test' contact and all multiples thereof. The transmission of ringing vcurrent `over c onductors S1 and 82 causes ring-dewn relay 94 to operate, the circuit extending from coli,-

ductor 81, back contact and armature ltll,`

upper Windingof ring-.down relay 941-, ,con-v denser 139, spring 135 of key K and its rest'- ing contact, hconductor 83, conductor Se und trunk conductor 82. Relay 94;, upon operating, at its armature 1,03 completes a locking circuit for itself, and at armature 1()2 coinpletes a circuit for the visual signal L to notify the attendant that a call is awaiting her attention.

rihe attendant operator, upon noting the lighted condition yoit' lainp L, answers the f by inserting plug.;` P into jacl; J The inf sertion of plug P into jack J, resulting in the closure rof jack springs 81, causes ground to be applied to conductor 87 independent of armature of relay 88.'` At the saine time a circuit is completed for sleeve relay' 169 el the cord circuit Q and relay 88 in sef ries. This circuit extends from ground, Winding of relay 169, sleeve contact 'of plug' P, sleeve of the jack J, and the Winding of relay 88 to battery. Relay 169, upon oper.- ating, at its armatures 171 and 172 reinoyes battery and ground from the tip and ring conductors of the cord and at the front een: tact oit' these armatures completes a direct current bridge across these conductors to cause the energization of the ring ,cutoff relay in the connector, which results in the talking connection being extended to the cord O.

Reley 88, upon operating, at its armature 101 disconnects polarized relay 8.6,` from in bridge of `the trunk, at this same arinutupe opens the initial operating circuit of ring.- down relay 94, and at armature 9.9 v opens .the locking circuit of `this relay. As n result, ring-down relay 94 deenergizes, causing the call signal lamp L to be extinguished.

The `attendant now ,operates her listening key K3 to connect hei' headset with the ,cord O so ,that she .may conuerse with the calling subscriber to ascertain the naine .or local .number of .the desired 5P. A. subscriber,

titl

ing ringing key gli. l Vseriber responds tollowingthe restoration o ii lt Will be assumed, in the present ease, that the subscriber at substation it is desired. The attendant will, accordingly, insert the plug)` I of her cord in the jack J. The cutoll relayv 1G is operated by the closure of springs 18st of the jack J when the plug P is inserted therein. The attendant now proceeds to signal the called station by operat- When the called subliey K'J a circuit for supervisory relay 159 is completed in series with the calling,` station and battery and ground supplied by the back bridge relay ot the connector in the M. n. X. Relay 1.55), upon operating, completes a circuit for relay lti. which also operates. Relay lo! at armature 1013 opens the normal A. C. bridge extending' across the tip and ring conductors ot the cord. at thel tront contact ot this armature connects a noninducA tive resistance in multiple with relay lfi.) to improve transmission. and at armature .loi opens a point in the ope ating` circuit ot' supervisory lamp li in order to prevent its` being lighted at this time.

lilhen the conversation between the tvo subscribers has been completed. the. replacement ot the. receiver at the callin;Y station brings about the rebase oi the various switches in the M. d.. X. Since the called partly. who in the present case is the l. .L Y.. subscriber. is still on the line. battery and ground tor maintaining the supervisory relay loi? operated, which was .supplied by the back bridge relay. oi the connector in the M. ik. X.. prior to release. inl now provided by battery and around connectiinis ot' the. line relay ot a selector switch. which is seized by the line switch in which the trualt normally terminates.

When the called subscriber replaces hir-1 receiver. the` circuit Ator supervisin'j.' relay laf? is opened. litt-.lay 155i. upon restoringopcnthe circuit ot relay loi which. upon renorinoj. completes a circuit for th:l .supervisocy lamp L to notify the attendant that' discon nection is .lesired. The withdrawal ol the plug; l" from the jack J" Aauses the re,` toration ot the cut-ott relay lo and rcstorat ion ot relay lt'i. The withdrawal of the pluxcr l" troni the associated jack results in the reste ration ol the armature ot relay loi) in the cord circuit. and in the deenergization oit' the visual .signal 12B. and relay titi in the trunli circuit. The relay SS. upon restoring. again connects the ring-down relay iliand the polarized relay Sti in bridge ole the trunl.

lelay SG inunediately operates. assuming that the M. A. X. connector has restored. and at itsy armature 9S opens` the circuit ol slow release relay This relay. accordingly. restores to remove thel busy condition troni conductor TQ extendinej to the multiple test contact accessible to the, selector repeater l) and other similar selectors. The trunk 'l' is now available tor use for extendingl connections ni either dlrcction.

(fof/.5' fromr ilf. ril. X. to!! operato/'s' o l. A. X.

Had the connection described in the l'oregoing been established by a toll operator in the M. A, X. the transmission of ringing current to the trunk conductorsl nl and l! would have been brought about by the toll operator operating her iii-,ual ringing lay. Otherwise. the operation would have` been the same except that. .-@ince the toil operator has facilities for applying rineincr current to the trunhY at will. the cord circuitsY at the l. X. are so arranged that7 should the toll operator din-.ire to recall the attendant alter the l. A. X. subscriber has. replaced his receiver, but bet'ore the attendant has pulled down the cord. .she may do so by operating;r her ringing key. 'lhisz will cause the alternating current rehj.' ,lofi in thc attendant:v7 cord to ope ate to complete a circuit for slov-c relea:=e relay lt'it. Relay ltji. upon operating at its iowcr armature open` a point in the ring conductor oll the cord to prevent the ringing current passing to the signalling;` device of the l. "1. subscriber. and at its upper armature completes a circuit l'or supervisory signal L. 'the lighted condition ot' this signal notities the attendant operator that the toll operator desires to communicate with her. The altcndant operator7 accordingly. operates` her listeningA key l. and (universes with the toll operator.

lt will now be assumed that, in the connection between the i?. A. X. and M. A. X. .--:ubseribers, it is desired to extend the ci ll to one or more other l. X. subscribers. li'nder these circumstances the l. ii. X. subscriber f-,ziniply actuatef,` his .switchlmok cau:- inf..r the supervisory lamp L to he tlashcd as a result of the periodic dccncrgization and energizaiion oli relays tot) and lb'i. 'l`hc attendant operator upon noting the flashing' of lamp l. immediately opi-ratei`- her listening hey lis. The attendant, a'lter no tityingjr theI subscribers ole her presence. will be informed of the other subscriber or sub scribers desired in on the connection. and a'l'ter receiving this information will restore her listening key to normal. '.l`he attendantl now sets up comun-tions to other l. A. X. subscribers in the same niauner that connection wasl made wiih the .subscriber at ub :4t ation A by inserting the. plugs ol' other cord corresponding to plut;l l ol' the cord circuit (iin the jacks .lin-JW. or other similar riaclzs in multiple therewith. not Fhuwn. 'l`hc conierence lie' K oil the trani; 'l` will now be operated by the attendant to connect the trunk'l to the conference jacks. lt should be bli liti

noted at this point that these jacks are preferably individual to an attendants position but common to a plurality ot' trunk lines. The saine is true of course of the tivo supervisory relays 92 and 93 and the condenser 140 as is apparent from the drawing, Fig. 2. The points Where other trunk lines, not shown, are connected have been denoted by arrows branching oil' troni the conductors which connect the conference jacks J1Jm and the relays 92 and 93 to the key K.

The operation oi key K in addition to connecting the conference jacks in bridge of the trunk conductors 81 and S2, at its springs 129 and 131 and their working contacts, at spring 130 and its working contact connects ground to conductor '72 extending to the inul'tipled test contacts terminating in the banks of the selector' repeater, such as D, and prepares a substitute holding circuit for relay 88 and busy visual signal 128 which becomes effective in case the originally established connection is broken While the conference is being carried von with other subscribers, as will be made clear subsequently. Key K also, at its spring 132 connects supervisory control relay 93 to grounded conductor 89. This relay, accordingly, operates to close a point in the circuit of lanip li.

It will be noted that the branch conductor connecting the ring conductor of the trunk T to the ring terminal ol the conference jacks includes a superi'fisory relay 92. This relay is, accordingly, energized to prevent the lighting of lamp L so long as any l). A. X. subscriber connected in on the cont'erence. However, when the P. A. X. subscribers in the conference all have reililaced 'their receivers relay 92 restores, causing supervisory lan'ip L to become lighted to intorin the attendant operator that the con terence has been terminated and that the coi'i'terence key K should be restored.` The restoration of this key eilects the disconnection ot the conference jacks troni association with this particular trunk, render-i Y them available for use in connection w yh any other trunk, reinoves ground troni conductor Z2 to render the trunk available 'to P. A. X. subscribers for outgoing calls, to cause the restoration ot the busy visual nal 128. and the relay 8S. Relay 88, upon restroing, reconnects the ringedown relay 911- and polarized relay S6 in bridge of conduce tors 81 and. 82 of the trunk T.

It inay often occur that the originally called l). X. subscriber, alter securing a number or other P. A. X. subscribers in on a conference, no longer needed in on the connection. Under lthese circumstances such subscriber' will replace his receiver, thereby informing the attendant, in the hereinbelore tescribed manner, that a disconnection is desired. 'll he attendant Will, accordingly, disconnect the cord O trein jack J3, and jack site direction to that normally supplied by' the outgoii'ig line switch, and, therefore, the

relay 85 ren'iains deenergized. However,

since at this tinie the conference key K is thrown, the closure otI armature and its back contact is ineffective to again energize relay 841. El substitute circuity for relay 88 and the visual signal 128 is now provided whichv extends by Way ot grounded spring 130 ot key l and its Working contact, conductor 7 2, arinature 95 and its back Contact, and the windings oi relays 88, 93 and visual signal 12S in multiple to battery. Relay 88 operates without ett'ectat this time, other than to disconnect the polar relay 86 from in bridge of the trunk.

Night service.k

service calls in this direction are handled as are the day service calls. f

Vllhen the attendant leavesfher position, honf'ever, she operates the night service keys K associated with the trunk T as Well as all other siniilar keys associatedfvvith the other trunks extending between the P. A. X. and M. A.. X.

The key l', when in its operated position, at its spring 13a and its Working contact supplies ground to conductor 91, thereby preparing a circuit for the direct current signals 1&2 and 143; at springs 133 and 137 disconnects conductors 1,411 and 145 from their normal connection With conductors 74 and TG, and connects these 'torlner conductors 'with trunk conductors 91, 82, and at spring 136 connects conductor 1115 with armature 96 of the relay Si and its grounded resting contact. lt will be appreciated from this that when the night service key is operated the facilities 'for callingthe attendant are cut out of service and the trunks normally accessible to trunks extending to the attend ants positionare inade busy by ground supplied by the resting contact and yarmature 96 of relay 84., being` ted back through Working contact and spring 186 ot the key K to the test conductor 79. It follows that if any subscriber' attempts to call the attendant the ,selector repeater will rotate its Wipers oil the bank and give the usual all trunk busy signal to the subscriber. Iey K also at spring135 opens the circuit for ringdoivn relay 911 so that it cannot be operated by ringing current transmitted to the trunk conductors S1 and 82. Howe fer, alternating Cil current relay 122, which is, in series with windings 126 and l2? ot the repeating coil R, is now in bridge ot' the conductors S1 and 82 and responds to any ringing, currentv transmitted thereover. llach time relay 122 is actuated it completes` a circuit `lor the common signals 1li, 1115, at its armature tuo, so that any Subscriber in the l. ft. X. upon hearing the operation ot any one ol thef-e signals` is informed that a l. A. X. subscriber is desired. Relay So also restores due to the reverse direction olf current supplied by the connector, and, in so doing, completes a circuit for relay Ell, the circuit ef-tendiug from grounded spring lill) ol key li and its resting contact, resting contact and armature 10U, resting' contact and armature flo, and the winding oli relay tl to battery. This. relay, upon ope ating, at its armature 05 supplies ground potential to test conductor 72 to make the trunk busy to 1.. A. X. Subscribers attempting to make outgoing calls, and at its armature titi removes the normal busy condition from the test conductor Til so that this truuk may be seized by a selector repeater' answer-im:r the call.

lt will be assumed that the subscriber at. sul'istation )t hars the signals lla! or 1-12'3 being operated and decides to answer the lall. 'llo do this the subscriber merely dials the digit t) which causes the selector repeater to position its wipersl opposite the tenth level ot bank contacts and to test. then lor the trunk seized which is identitied trom the idle trunks by the ground having been removed from its test1 contact. As ,soon as the wipers of the selector repeater' engage. the spring contacts (3l, (35 and titl the selector repeater switches through in the usual manner, and in so doing renders this trunk busy to other similar switches. Since the selector repeater places a direct current bridge across conductors TS and S0. relay 122B in the trunk circuit is energized. 'This rela)T upon operating completes` a circuit ler relay 121 which. at its arnniture 105, places a direct current shunt; about relay 122 which causes the ring cut-oil' relay in the connector ot' the Bl. X. to energize to cut olf the ringing current and to Iswitch the connector into talking position. Conversation may now be carried on through the repeating coil lt.

.lt will be noted that although the ringl cutofi' relay o't the tonnect'or removes ringing current. lrom the trunk coiuluclors Hl, b2, since the signaling devices Y112, lfl-' are common to all incoming trunks. these signals continue to operate as long as there is a all on any trunk awaiting the attention ol a l. A. X. subscriber.

lVheu the conversation is completed the calling subscriber.v in replacing his receiver. causes the switches in the M. A. X. to be restored in the usual and well known manner,

while the replacement of the receiver at the substation A causes the line :switch C, selector repeater D, and the arioua ope 'ated relays in the trunk T to be restored to normal in substantially the saine manner as described wlien a connection was set up to the attendant. operator. Ul" course, since the key ii in operated position the deener- -iyauion ol' relay Htl again renders` the tonuciors 7F. 75l and 8() busy to the selector 'epeater l.) until a trunk is again taken l'or ne by :n \l. X. subscriber.

ll the l. it. X. :szubscribe' who answered the call is other than the desired party, the l. A. subscriber may request the M. A. X. subscriber to hold the wire until the desired subscribe answers. 'llhe l. A. X. .subscriber then replaces hie receiver, 'arising the line and release relayfsV lill and A121 to restore. rl'he l. A. 1x'. subscriber now gets in touch with the desired subrecribcr who will proceed to connect with the trunked line in the same nainner as did thesubscribe atsuhstation A; 'the trunk having been rendered accessible io a #elector repeater, .such as l), upon the release oll the selector l).

ln certain installatifms, it may prove more desirable to require a desired subscriber to use the .subscriber-'s telephone who answers the incoming night call. For it will be apprecattal that in the arrangement. juat. described, :should the. incoming lrallic be rather heavy, there is a possible chance that, a dewired l". Xt. X. subacriber. in attempting:r to .set np a mnneeion with a trunk call answered by .some other subscriber, may obtain, instead, connection with a trunk which has not previously been answered.

ly connectingr the relays ol Fig. l into association with the trunlt 'l by attaching terminals 10T lo lltl, inclusive, to terminals lo to 11d. respectively. the operation will he so changed that. when the original answern ing l). It. X. snbacriher replaces the receiver at .substation A, the trunk '.l` will be main tained luisy to all l). A. X. subncribers until the al. A. X. subscriber restoreel his receiver, making il. necessarf.' for the desired l). A. X. subscriber to use the telephone ot the subscriber answering the -all. The operation is as Follows: When the subscriber :1t substation .it replaces his receiver, raining the release ot line relay 123 of the truuk T, an impulae is transmitted from the grounded armature olf relay 122% and its resting eontact. armature ltlt and itis \\orking contact, terminals` 10H and lou. and the winding of relay V115 to lnittery. This relay ope-ales and a moment later. upon restoration of relay 121. a circuit is connilettal ilor slow relay 1172 l'rom grounded arn'uiture and back contact of relay 123, armature 10G and its back lll) tor TS) to p u: the seizure of the trunk by a i). Si. X. subscriber prior to its release' by the iai. X. subscriben` This' method' of operation also guards against possible' trouble which might' result if the first* trunk ot' the group is held infuse' for an unusual period by some M. A'. X.` subscriber. i"inally, when the connection is released by the iii. A. X. subscriber, resulting-"ihl the" normal battery and ground potential2 supL plied by the line switch being again appliedy to conductors 81 andSzZ, relay S'Gfagaineiiergizes, thereby causing the restoration of slow release relays Set and 112.' Relay 84", upon' restoring, at its armature 9G again places' ground on the priyate conductor 79 tor'eplace that formerly supplied by armature 11i oi" slow releas'e'relay 112;

in certain installations where thelpri. X'.l is a very short distance from the'Ml A. Xe it may `prove more economical to'utih/i'e'ordi` nary tirst selectors in substitution :tor sel f oi" repeaters such as" D. This may be done without necessitating any changes 'in the trunk' circuit T, either with' or without the inodii'ication shown in Fig. il In the" use of a selector when thev trunl-T is'seized,A

relay 121 at its arii'iatilre 10er` applies grouiid to conductor 'T9' t'o maintatin the selector" and line switch in operated position.

W'hen the trunlicir'cuit' is used niodihed by the addition of Figi el, it is essentiahthat,` in order to permita P'. A. X. subscriber to' release from the trunk independent" of the iii. A. X. subscriber, ground potential `tor maintaining the selector' and line sWitch oi' the calling line be removed. This is taken care ot by relays' 1'12' and 121i y It will be noted that there is al short intervai between the deenergization of relay 121 and the energization of relay 112,' (relay 112; being slow to pull up) during which no ground potential is present on test coductor 79. This interval is Very short butV is suiiicient to allow the selector to respond so that it and the line'switch of the calling line will restore.

.Having described a system in which," are' incorporated the various" features, which'A are considered new and on which LettersPatent is desired, these features'willy now'v be pointed' ont in the appended claims.

lVhat is claimed is: 1. in a telephone system, private and main automatic exchanges', trunk lines interconnecting said exchanges, an attendant operators switchboard equipped with facilv` `ities for manually answering and` extenlillngVV connections" from` said' trunk lines to i subscribers ot the private autoniatic exchange, a' set' of callsignals coi'ninon to said trunks, mannu'ally operable night service leys,there beingone such liey for each trunk, means rendered' eii'ectitve jointly by theoperation oi a key and the seizure of a corri-ispondihg truuk t'or rendering the sume accessible to any substation oi theprivateY automatic exchange', andn'ieaus reinlered eilective a flow' oi" signalling current transmitted from the main exchange lorfcausingthe operation of said" call/ signals.

2'. In a telephone system, main and private' automatic exchanges, trunk lines interconnecting'said exchanges, an automatic switch havin'gf direct, access to said' trunk lines via two' paths', means for making said trunlt4 lines' busy,- n'ieans for rendering said' trunk lines'inaccess'ibl'e via one of said paths when the trunks are idle,andmeans for rendering'said trui'ils inaccessible to said automatic switch` via the other path when said' trunlr lines are' in use.`

In a' telephonesystem, mainand private automatic exchanges', trunk lines interconnecting' said exchanges, an automatic switchf having direct access'to said trunk lines over' apluia'lity paths, and means for preveiiting said` automatic switch from seizing one of' said trunks over aparticular path unless the trunli-y already been taken ior'l usef ill'n atel'ep'hone systenn'main andprivate' automatic exchanges, trunlchnes intercona n necting said' exchanges,l an attendant opera' tor" switchboard at the tprivate automatic exchange equipped withiacilities for manually exteiiding connections to subscribers of the private automatic exchange, av plurality of conference' acks individual to the atteiidents position but cominoir tosa'id' trunk lines, means at the attendant operator-s position for setting upconnections to a plurality oii subscribers oi the private automatic ex"- change a'nd for connecting said subscribers lineswith4 said jacks, and means associated witliitheinter-exchange trunk in use'ior sini'- ultaneously' connecting said privi'te auto'- i matic exchange subscribers lines in talking relation with said trunk line. p

5.y In' a telephone systeni, an automatic switch, other automatic switches` accessible thereto; means for transmitting in'ipuls'es tb said iir'st automatic switch to cause the same to select another automatic switch,` an inipulse repeating devicein said ii'rst auto'- matic switch including an impedance ele#` ment, and meansfo'r includiirg a non-inductive resistance in multiple with said impedance" only during the" transmission of imA pulses' to" said second automatic switch to prevent an extra' impulse' being transmitted by the pulsing relay thereof 'the end ot an imp'ulse'series.

o. In telephone system, an established lill connection between a private automatic exchange subscriber station and a toll operator including a cord circuit, a signalling device at said subscribers station, means in said cord etl'ective upon the replacement of the receiver by the private automatic exchange subscriber' for signalling an attendant ope ator at the private automatic exchange, a second signal in said cord, and means placed under control of the toll operator for operating said second signal to call the attendant, said last means also etlective to prevent the signalling device ot the private antomatie exchange subscriber being operated by the toll operator.

T. In a telephone system, an established connection between a private automatic exchange subscriber' and a subscriber ot a main automatic exchange including a cord at an attendant operators position in the private automatic exchange, a supervisor;v .signal provided t'or the subscriber in the private automatic exchange for giving an attendant operator disconnect supervision, and means controlled by the subscriber in the main automatic exchange for causing said supervisory signal to be flashed when an attendant operator is desired in on the connection.

S. In an impulse repeater, an impulse repeating relay, an impulse repeating circuit including contacts oi' said relay, an inductive resistance normally included in said circuit, a non-inductive resistance, a second relay having contacts for connecting said non-inductive res' tance in multiple with said inductive resistance, and means controlled b v said first relay Jfor causing the operation of said second relay while impulses are being repeated.

9. In an impulse repeater', an impulse repeating circuit including an inductive impedance element, a non-inductive resistance, and means for including said non-inductive resistance in multiple with said impedance only while impulses are being repeated.

l0. In a telephone system, an inter-ottico trunk connecting a first with a second auto matic exchange and terminating at the first exchanee at an operators position, subscribers lines in said first exchange, a common signal device for said lines, a relay and a condenser' bridged across said trunk, said relay being responsive to a flow ot' signalling current applied to said trunk at said second exchange to operate a signal at said operators position, a manually operable switching device associated with said trunk, and means for simultaneously signalling said subscribers lines at said first exchange by operating said common signal device when said switching device is operated and signalling current applied to said trunk at said second exchange.

11. In a telephone system, private and main automatic exchanges, trunk lines interconnecting said exchanges, an attendant op erators position at said private exchange. a set oi call signals common to .said trnnlt` and to all subscribers of said private exchange, a` manually operable switching device associated with cach trunk. and means rendered etl'ective jointly by the operation of said switching device and b v a flow of signalling current transn'iitted from the main exchange over a trunk line for operating said call signals.

1Q. In a telephone system. main and private automatic exchanges. trunk lines` inter connecting said exchanges, an automatic switch having terminals arranged in hori zontal levels, said switch having access to said trunk lines via two levels, means` for making said trunk lines busy. means for rendering said trunk lines inaccessible via one ot' said levels when the trunks are idle, and means tor rendering said trunks inaccessible to said automatic switch via the other level when said trunk linesy are in me.

i3. In a telephone sistem, main and private aiuomatic exchanges, trnnl; lines interconnecting said exchanges, an alitoinatic switch having terminalsy arranged in horizontal levels, cach ot said trunh line.,` connected to two ot.: said levels, subscriber controlled means for operatn ing said automatic switch to seize ontl of' said trunk lines over a certain level to extend a call, and means for preventing .said automatic switch from seizing one ot .said trunk lines over the other level unless the trunk has already been taken for use..

l-l. In a telephone system, a first and a second automatic exchange, trunk lines interconnccting said exchanges, an automatic switch at said first exchange having terminals arranged in horizontal levcls.cach of said trunk lines connected to two otl said levels, subscriber controlled means for operating said automatic switch to .seize one ot' said trunk lines over av certain level to x tend a call trom said first to said second exchange, and means for preventing said automatic switch from seizing one ol' said trunk lines over the other level unlessthe trunl; has ah' aidy been taken tor use by a subscriber extending a call from .said second to said first exchange.

15. In a telephone system, a first and a second automatic exchange. trunk |ine.-:y interconnecting said exchanges, an automatic switch at said first exchange having direct access to said trunk lines over a plurality ol' paths, means controlled b v calling subscriber for operating said automatic switch to seize one of said trunk lines over a certain path to extend a call l'rom said lirs to said second exchange, and means for preventing said automatic switch troni :cizing one off said trunk lines over another patti unless the trunk has already been taken for ll fr litri invase? switch having direct access to said trunk lines" overI a plurality ot' pat-hs, and means iii saidiiiist exchange for permitting the' seizure' ofon'e noiE said trtinl lineso'ver4 a certain oi saidlpathsjnly its' id trunlt line has already been' tal',` n" for use' i the extension oi a call from saflidsecoiid" to said li'rst exchange.

i8". In a telephone system, main and private automatic exchanges, an automatic switch having terminals arranged in groups in horizontal levels, trunk lines interconnectign said exchangesgeach' oi'` said trunk lines connectedA to av plurality et said levels, and means for preventing saidautomatic switch from establishing connection with one ot said trunk lines Overa particular level unless the trunlt has already been" taken for use.

19. In a telephone system, main and private automatic: exchanges, trunk lines interconnecting said exchanges, an attendant operators switch-board at the private automatic exchange equipped with facilities for manually extending connections to subscribers ot the private automatic exchange, a plurality ot conference jacks and supervisory relays individual to the attendants position but common to said trunk line, means at 'the attendant operators position for setting' up connections to a plurality of Subscribers ot the private automatic exchange and for connecting said subscribers lines with said jacks, means associated with the inter-exchange trunk in use for simultaneously connecting said private automatic exchange subscribers lines in talking relation with said trunk line, and means operated by said supervisory relays upon the last private automatic exchange subscriber withdrawing from the connection for signalling said attendant.

20. In a telephone system, a first and a second automatic exchange, trunk lines interconnecting said exchanges, manually controlled means at said first automatic exchange including a plurality oi conference jacks for connecting a plurality of sub`v scribers lines to a trunk, means associated with said trunk for simultaneously connect ing said subscribers lines in talking relation with said trunk line, supervisory means rfi common to said trunk' lines` and f associated withy saidJl conference jacks', and means' op,` erated by saidsupervi'sory means uponthe last subscriber connected to said conference signalling the attendant.

jacks withdrawing from the connection iior' .ln4 a telephone systeuuytirs't and se?` ondl5 automat-ic exchange trunk lines inter? co'iinectiiigfsaid*exchanges, said trunk lines terminating" at said iirstf aiitonu exchange iiir individual` jacks at an attendant oper-y ators switchboard, a plurality ot auxiliary jacks coiniiion to said trunk lines 'for courlectingal plurality' ot s'ubscribei's7 lines to'ra" trunk, means associated with" said; tr nls tor simultaneously 'connecting sait subs rib# ers rlines in talking relationwith4 said truuk lines, supervisoryrelays eznnnion to" said tifiiiil; lines and associated with saldi confereiice' jacks, and means operated by said supervisoryy relays when the last subscriber withdraws 'from the connection" 'set up over said conference jacks `toi" signalling the ati tendant. i

In a' telephone systeil, an automatic switch, other auton'iatic switches accessiblethereto, meansk for transmitting impulses to said iirst1 automatic switclitofcause the same to select `another autonuitic switch, an im# pulseV repeating device in said lirst' automatic switch including an impedance element and a non-inductive resistance,` said resistance normally out ot circuit, and means 'for including said non-inductive resistance in parallel to said impedance only during the transmission of impulses to succeeding switches.

23. In a telephone system, an automatic switch having access to other automatic switches, means tor transmitting impulses to said first automatic switch to establish connection with succeeding automatic switches, an impulse repeating device in said first automatic switch including` an impedance element and a non-inductive resistance, and means for including said lnoneinductive resistance in parallel to said impedance only during the transmission ot impulses to succeeding switches.

E24. In a telephone system, a private automatic exchange, subscribers stations thereat each having a signalling device, a main exchange, an attendant operators position at said private exchange, a toll operators position at said main exchange, an established connection between a private automatic exchange subscriber and said toll operator including ay cord circuit, means in said cord circuit effective upon the replacement of the receiver by the private automatic exchange subscriber for signalling said attendant operator at the private automatic exchange, a second signal in said cord circuit, means op erable by ringing current applied by said toll operator to the talking conductors of said cord to recall the attendant, and means for preventing the operation of the signalling device or' the connected private automatic exchange subscribers substation during the time ringing current is applied by the toll operator.

ln an automatic telephone system, a tirst and a second exchange, subscribers lines in said lirst exchange, an attendant operators position in said lirst exchange, a toll operators position in said second exchange, an established connection between a subscriber at. said first exchange and said toll operator at said second exchange including a cord circuit, means in said cord circuit opcrable upon said subscriber withdrawing l'rorn said connection for signalling said attendant operator at said iirst exchange and for closing an A. C. bridge across the line conductors leading to said second exchange, a second signal in said cord circuit operable by ringing current applied by said toll operator to the talking conductors ot said cord to recall said attendant, and means tor preventing the transmission of ringing current to the subscribers substation.

26. ln a telephone system, main and private automatic exchanges, trunk lines interconnecting said exclianges, an attendant 0perators position at the private automatic exchange, asubscriber controlled automatic switch having access to said trunk lines and to said operator-s position over two distinct paths, means at said operators position for receiving calls from the main exchange and i'or extending them manually to subscribers of the priv'ate automatic exchange, a manually operable night service liey at said operators position, and niet ns actuated by said key to permit subscribers oll said private automatic exchange to establish connection with a calling main exchange subscriber by means of said automatic switch and over said path normally provided l'or calling the attendant operators position.

2T. ln a telephone system, an established connection between a private automatic exchange subscriber and a subscriber ol' a main automatic exchange including a cord at an attendant operators position in the private automatic exchange, and supervisory means in said cord jointly controlled by the private and by the main automatic exchange subscriber l'oil giving disconnect supervision upon the private automatic exchange subscriber withdrawing l'roin the connection and tor recalling the attendant by flashing upon the main automatic exchange subscriber intta-mittently operating the switch hook.

ln witness whereof, l hereunto subscribe my naine this 30th day of December, A. D., 1924'.

CLARENCE E. I OMA X. 

